Process for producing a porous vinyl ester



United States Patent 0 PROCESS FOR PRODUCING A PORUUS VliNYL ESTER HarryA. Touimin, Jr., and William R. Stauifer, Dayton, Ohio No Drawing.Application February 9, 1953, Serial No. 345,226

2 Claims. (Cl. 260- 25) (Filed under Rule 47(a) and 35 U. S. C. 116)This application is a continuation-in-part of the application filed inthe names of Harry A. Toulmin, Jr. and William R. Stauifer, Serial No.32,736, filed June 12, 1948, now U. S. Patent No. 2,659,703, andentitled A Method of impregnating a Synthetic Rubber To Form a SpongeRubber and the Article Produced Thereby.

Our invention relates to the production of sponge rubber and inparticular to the production of rubber foam to form vulcanized foamrubber products.

it is our object to provide a method of production of rubber sponge fromlatex, either natural or synthetic, and in the course of such productionto prevent the coagulation of the rubber which increases particle size.It has been found that, while the pH value can be controlled for thispurpose, yet the average size of the particles increase regardless ofsuch precautions exercised in preserving the latices.

When latex is impregnated with nitrous oxide, particularly syntheticlatex such as that made of neoprene, it has been found necessary to coolthe neoprene latex in order to prevent coagulation in the bomb. Asnatural latex ages and becomes more unstable, it foams less and tends tocoagulate more in the bomb. In order to prevent natural latex frombecoming unstable before it can be used, refrigeration has been resortedto, although this is undesirable for various reasons including cost anddifficulty in mass production.

We have found that the addition of sodium silicate solution in aquantity of up to of the volume of latex prevented coagulation andeliminated the necessity for refrigeration. Additionally, the use of thedecelerating sodium silicate, which counteracts sodium silicofluoride(NaSiFs) added to such latices as a dormant coagulant or sensitizer,resulted in balancing the reaction with the latex so that when it wasimpregnated with nitrous oxide to aerate it and cause it to foam, therewas no necessity for refrigeration and there was no coagulation. Animproved product and one of much lower cost resulted thereby, the latterbeing due to theelimination of refrigeration and to the substitution ofthe cheaper sodium silicate for more expensive materials.

The sodium silicate used was supplied by the Philadelphia QuartzCompany. It was grade PQ-N and had the following analysis:

Percent SiOz 28.7 Nae. 8.9 H20 624 Varying amounts of this sodiumsilicate were added to, for instance, neoprene latex. There was nocoagulation inlatex samples which contained relatively la'fge amounts(20% by volume) of the silicate. With '.15 cc. .of 'PQN sodium silicateadded to 100 cc. of neoprene latex compounded withplasticizenzcoagulation took place one minute after the sensitizer was2,802,796 Patented Aug. 13, 1957 "ice added. When the amount of sodiumsilicate was increased to .23 cc. per cc. of neoprene latex (otherconditions being equal), the latex did not coagulate, but remained aliquid which, however, contained grains of solidified rubber. 1

By using the nitrous oxide method of foaming on compounded latexcontaining various amounts of sodium silicate, we have been able to foamthis latex without using refrigeration.

By the methods used by us heretofore, the foaming of latex is done intwo operations, first, adding the plasticizer and sensitizer to thelatex while stirring, and second, incorporating nitrous oxide (N20)under pres-.

sure at 200 p. s. i., and releasing the pressure by bleed ing the latexout of the bomb, when the latex is-foamed by the release of dissolvednitrous oxide. These operations are usually carried out at about 4 C.,which means refrigerating the latex bomb, and accessories for severalhours before experimental runs and keeping the temperature at this pointduring the runs.

'Under our invention, the Waring or mix-blender is used. This is a typeof high speed stirring machine (12,000-15,000 R. P. M.) in which theincorporation of the nitrous oxide, with resultant foaming, and additionof plasticizer and sensitizer can be accomplished all in one operationin about three or four minutes, and the foamed latex poured directlyinto a mold for curing.

By the use of theblender, and the speed stirring, coagulation is stillmore delayed. This is another factor responsible for eliminating thenecessity of refrigeration. The foaming is carried out in one operationinstead of the two operations used in the previous methods.

By this method we can eliminate entirely the use of a bomb or closedchamber for the impregnation of the latex with nitrous oxide, althoughthis process works successfully with a bomb or autoclave. One of thedifficulties in the use of latex, particularly neoprene latex, for themaking of sponge rubber has been its great sensitivity, especially afterthe sensitizer has been added. This has also been overcome by theinstant process.

Example N 0. 1

Neoprene latex foam was prepared as follows:

50 gms. of neoprene latex (#22087) were foamed to cc. by introducingnitrous oxide, and then 10 cc. PQ-N grade of sodium silicate were added.There was no coagulation within 5 minutes, the foam became smooth andthe bubbles became fine. When 1.2 cc. of sensitizer 40-2 was added, thelatex became grainy.

Neoprene latex #14022087 (an aqueous dispersion of neoprene rubber...50to 55% by weight neoprene) gms 50;0 Plasticizer #304 (low viscositycastor oil cc /2 Sodium silicate PQ-N cc 0.0 Sensitizer #40-2 (25%dispersion of sodium silico fluoride) cc 1.0

with thorough mixing after each addition, and foaming with nitrousoxide, coagulation required of a minute after the sensitizer was added.With 2 drops (0.152 cc.) of PQN sodium silicate, the coagulation timefor the foam was one minute, with 3 drops (0.228 cc.) of PQ-N sodiumsilicate, the latex did not coagulate and also with'4 drops (0.304 cc.)of PQ-JN sodiumsfilicate; there was no coagulation. These two samplesthat did not coagulate were cured in a 200 F. oven for 1 /2 hours. Thesponge contained a large amount of small bubbles that werewell'dispersed. j

The plasticizer is a vegetable oil and the foaming agent is a soapsolution.

Example N0. 2

Neoprene latex at room temperature (75 F.) was compounded as follows:

Neoprene latex #14022087 (Example 1) gms 600.0

Plasticizer #30-1 (Example 1) cc 12.0 Sodium silicate PQ-NL; cc 13.5Sensitizer #40-2 (Example 1) cc 13.8

There was thorough mixing after each addition, N20 was dissolved at 200p; s. i. for 3 minutes, the latex was bled from the bomb and allowed tofoam. This foam was cured in an oven of 250 F. for 1% hours.

In these examples the latex compound 14-0-220S7 is a product of AmericanAnode, Inc, of Akron, Ohio, and is a polymerized chloro2-butadiene 1,3,comprising 53 to 54% solids. The latex contains 88% neoprene on the drycompound and has the further following characteristics: a pH of 10.5 to11.0; a viscosity #2 Zahn in seconds of 16-22; and a specific gravity of1.13 to 1.16.

Therefore it will be seen that it is possible by the use of sodiumsilicate to eliminate refrigeration and by the foaming of latex with amixer blender at high speed of from 12,000 to 15,000 R. P. M. toincorporate the nitrous oxide; it is also possible to omit the closedchamber or bomb otherwise employed for impregnating the latex withnitrous oxide up to 200 pounds per square inch. This again effects agreat saving in time and overcomes the difliculty of handling.

After the aerated latex has been formed, the sponge is vulcanized insuitable shapes in open molds or in sheets as may be desired.

This method provides a sponge with a wide dispersion of bubbles ofuniform size and disposition which gives a highly resilient but strongsponge rubber. t makes it possible to deliver the foam material wheredesired through pipes. As has been mentioned before, it also eliminatesall refrigeration, closed molds and pressure bombs, thereby bringing thecost of sponge rubber down to a point where it can be economically andwidely used. The regular curing time of the foamed rubber product is 1/2 hours at an oven temperature of 250 F. We then wash the sample firstwith cold tap water until no foam is exuded on squeezing, then rinse bysqueezing for about five minutes in 1% hydrochloric acid. Thereafter thehydrochloric acid is removed by washing the sample in cold runningwater, again by squeezing it for about five minutes. Thereafter wesqueeze the sample as dry as possible and cure further for one and ahalf hours at 250 F.

While natural as well as synthetic rubbers or their mixtures areapplicable for the invention, neoprene, polyvinyl chlorides, vinylideneand butadiene latices are especially satisfactory.

Examples illustrating vinyl resinous compositions suitable for foamingas in Examples 1 and 2 are as follows:

Example N 0. 3

Polyvinyl chloride gms 500-600 Plasticizer (Example 2) cc 8- 12 Sodiumsilicate (Example 2) cc Sensitizer (Example 2) cc 10- 15 Example No. 4

. In this instance the composition was compounded as m Example No. 3except vinylidene chloride was substituted for polyvinyl chloride.

Example N0. 5

' The composition foamed in this instance was made up as in Example No.3 using methyl vinyl ketone in place of polyvinyl chloride.

Example No. 6

In this instance methyl vinyl ether is used in lieu ofpolyvinylchloride.

Example N0. 7

in this composition a 1:1 by weight mixture of polyvinyl chloride andvinylidene chloride is used as the resin ous substance for making afoamed base material as illustrated in Example No. 3 Various mixtures ofthe vinyl resinous compounds may be used or in conjunction with suitableproportionate amounts of neoprene.

Example N 0. 8

The vinyl resin used in this instance is polyvinyl acetate which issubstituted for polyvinyl chloride in Example No. 3. The plasticized andsensitized resin is then expanded to form a foamed resinous material asdescribed.

Vinylite resins, for example polymerized vinyl chloride, asaforementioned, may be substituted directly for neoprene latex asemployed in Examples 1 and 2. Such polyvinyl compounds as well ashomologues thereof may also be used.

When a closed chamber is used, the mixture is impregnated at from 25 to250 pounds pressure with nitrous oxide: then released after shaking,stirring, etc. and it foams as released. Thereafter it is vulcanized inthis foamed condition.

Under either method, with or Without an autoclave, the sponging takesplace in the open air and is vulcanized in that condition. The foam willstand from a few minutes to several hours without material change.

it will be understood that we desire to comprehend within our inventionsuch modifications of the apparatus and method and substitution ofmaterials as may be fairly comprehensible within the hereinafterappended claims.

We claim as follows:

1. In a method of manufacturing sponge rubber, the steps comprisingmixing polyvinyl acetate, sodium silico fluoride and sodium silicate inthe proportion of substantially one part by volume of a 25% dispersionof sodium silico fluoride sensitizer and substantially one part byvolume of sodium silicate of the approximate composition SiOz 28.7%,NazO 8.9% and H20 62.4%; introducing nitrous oxide under pressure intothe mixture, releasing the pressure on the mixture impregnated withnitrous oxide to produce a foamed rubber mass, and curing the foamedmass by the application of heat, the polyvinyl acetate and mixture ofsilicate and sensitizer being present in the proportion of about 600grams polyvinyl acetate to 30 cc. of the mixture of silicate andsensitizer.

2. In a method of making sponge rubber which consists of mixing thefollowing ingredients in the proportionate amounts as follows:

Polyvinyl acetate gms 500600 Plasticizer castor oil cc 8-12 Sodiumsilicate cc 10-15 25% dispersion of sodium silicofiuoride sensitizer cc10-15 References Cited in the file of this patent UNITED STATES PATENTSRe. 23,697 Stauffer Aug. 4, 1953 2,640,087 Borton May 26, 1953 2,659,703Toulmin et ai. Nov. 17, 1953 2,666,036 Schwencke Jan. 12, 1954 OTHERREFERENCES Bakelite Review, Schwencke, July 1952, pages 20 and 21.

Vinylite Resins; Bakelite Corporation, copyright 1944, page 5.

1. IN A METHOD OF MANUFACTURING SPONGE RUBBER, THE STEPS COMPRISINGMIXING POLYVINYL ACETATE, SODIUM SILICO FLUORIDE AND SODIUM SILICATE INTHE PROPORTION OF SUBSTANTALLY ONE PART BY VOLUME OF A 25% DISPERSION OFSODIUM SILICO FLOURIDE SENSITIZER AND SUBSTANTIALLY ONE PART BY VOLUMEOF SODIUM SILICATE OF THE APPROXIMATE COMPOSITION SIO2 28.7%, NA2O 8.9%AND H2O 62.4%; INTRODUCING NITROUS OXIDE UNDER PRESSURE INTO THEMIXTURE, RELEASING THE PRESSURE ON THE MIXTURE INPREGNATED WITH NITROUSOXIDE TO PRODUCE A FOAMED RUBBER MASS, AND CURING THE FOAMED MASS BY THEAPPLICATION OF HEAT,THE POLYVINYL ACETATE AND MIXTURE OF SILICATE ANDSENSITIZER BEING PRESENT IN THE PROPORTION OF ABOUT 600 GRAMS POLYVINYLACETATE TO 30 CC. OF THE MIXTURE OF SILICATE AND SENSITIZER.